When did the first civilization develop in mesopotamia?

There is a common reference to the Ubaidians being the first civilization. The Ubaidians had migrated to the Tigris-Euphrates river valley (alluvial plain) from the steppes of northern Mesopotamia (Assyria) c. 4600-4800 BCE. Their adaptation of irrigation led to enough food production to support a larger population and their farming villages led to small cities, with natural boundaries creating city/states. The practice of religion and forays into warfare supported the appointment of priests and warrior chieftains which ruled the city/states. The creation of other trades beside farming and organized religion led to the consensus that this was civilization. However, further excavations at tel Halaf predate the Ubaidians so who knows? Archaeological study of the near east is a relatively new development for that area, and new finds rewrite their history repeatedly. Also, it is considered that the Egyptians were the first civilization.